Field of the Invention
The present disclosure relates to a filter unit for a canister. More particularly, it relates to a filter unit for a canister which can prevent a filter from being clogged with dirt or powder (canister active carbon powder) and can reduce bleed emission under regulations about evaporation gas.
Description of Related Art
In general, the fuel system of vehicles using gasoline fuel in vehicles includes a fuel tank that keeps fuel, a fuel pump that pumps the fuel in the fuel tank to an engine, a fuel filter that removes foreign substances in the fuel supplied to the engine, and a fuel line that guides the fuel to the engine.
Meanwhile, gasoline fuel produces a large amount of fuel evaporation gas due to evaporation (Hydrocarbon gas, hereafter, referred to as an HC gas) and it causes a loss of fuel and contaminates the atmosphere.
Accordingly, a canister that collects and keeps an HC gas generated from a fuel tank is necessarily used in order to solve this problem.
A canister 10, as illustrated in FIG. 1, is achieved by filling a case 11 having a predetermined volume with an adsorptive substance that can adsorb an HC gas evaporating from a fuel tank keeping gasoline fuel, in which an activated carbon 16 is generally used as the adsorptive substance.
The canister 10 adsorbs an HC gas on the activated carbon 16 with an engine stopped, but when the engine is in operation, the HC gas adsorbed on the activated carbon 16 is diffused by the pressure of air taken inside through an air port 12 and supplied to the engine along a fuel system through a purge port 13.
However, according to FIG. 2 illustrating operation of a canister 10 of the related art, while air flowing into an air port 12 passes an air filter 15 and discharges an HC gas adsorbed on activated carbon 16 in the canister 10 through a purge port 13, with a vehicle driven, foreign substances in external air clogs the air filter 15.
According to FIG. 3 illustrating operation of a canister 10 of the related art, when air in a fuel tank is discharged to an air port 12 through a load port 14 in fueling, powder of activated carbon 16 passing through the canister 10 clogs an air filter 15.
In these two cases, when the air filter 15 is clogged, explosive vibration by an engine is fully transmitted to the fuel tank, so the fuel tank cracks and air cannot smoothly flows inside, which causes frequent stop of the engine.
Accordingly, when the air filter 15 of the canister 10 is clogged, it is required to replace the canister for the safe of the vehicle, so the maintenance cost increases.
With an increase in environmental pollution, recently, many countries have enhanced evaporation emission regulations and tailpipe emission regulations as well.
The evaporation emission regulations regulate emission of an HC gas from a fuel tank of a vehicle to the atmosphere due to natural evaporation in order to reduce environmental pollution by minimizing a loss of fuel naturally discharged to the atmosphere when a vehicle is stopped/parked and driven as well.
A typical part for the regulations is the canister 10 that most effectively reducing an evaporation gas.
However, the canister 10 of the related art, as illustrated in FIG. 4, when the activated carbon 16 in the canister absorbs an HC gas and the concentration increases, an evaporation gas is necessarily diffused by the difference in concentration in the canister 10. Further, when the capacity of the canister 10 is small, bleed emission (hereafter, referred to as ‘BLEED EM’) increases.
In this case, it is effective to increase the amount of an HC gas that can be collected, by increasing the capacity of the activated carbon 16 in order to reduce the BLEED EM of the canister 10, but the cost increases and the size of the canister increase and the canister is difficult to be mounted, so this method is not used.
In order to reduce BLEED EM by increasing the cross-sectional area and the length of a passage through which an evaporation gas passes, it is possible to install a separator or insert a cylindrical pipe, but in this case, ventilation resistance increases and spit back, a phenomenon that fuel flows backward in fueling, is caused.
Accordingly, the HC gas that is not adsorbed on the activated carbon 16 is easily discharged to the outside through the air port 12, so the evaporation emission regulations are not satisfied due to BLEED EM.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.